package p1000;

import java.util.Scanner;

public class Main1001求和 {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        while (input.hasNextInt()) {
            int n = input.nextInt();
            int sum = 0;
            for (int i = 0; i < n; i++) {
                sum += (i + 1);
            }

            System.out.println(sum);
            System.out.println();
        }
    }
} 